A superconducting transformer (1) comprising a core coil assembly (2) comprising superconducting material windings (3) mounted over a magnetic material core (5). The core coil assembly is located in an inner housing (6) of thermal conductor material. The inner housing is located in an outer housing (7) of galvanised fibre reinforced plastic in spaced apart relationship. The space within the inner housing and the space between the inner housing and the outer housing is evacuated and the space between the inner housing and the outer housing is insulated with thermal insulation material (8). The transformer further comprises at least one cryocooler (9) for cooling the core coil assembly at subzero temperatures (Fig 1)